(1) Field of the Invention
One aspect of the invention relates to an impact-receiving surface such as a helmet supported by a multi-stage energy absorbing liner system that progressively receives and redistributes energy generated by an impacting force.
(2) Description of Related Art
It is known that energy equals force times distance. In the case of impacts sustained by the head or other anatomical member, impact forces and impact energy translate into accelerations with both linear and rotational components. Such accelerations are experienced by the brain and brain stem during and after an impacting event. In an attempt to minimize such impact forces, energy absorbers are deployed for example in helmet systems in an attempt to reduce the forces and resultant percussive loads experienced by an underlying mass, such as the brain.
The effectiveness of any energy absorbing system depends on its relative stiffness and crush efficiency over the range of impact energies the system is expected to experience. The ideal force displacement response for linear impacts has a relatively “square wave” shape. Idealized square wave energy absorbers ramp up quickly and maintain a relatively constant load throughout the impact event that maximizes the amount of energy capable of being absorbed. The ultimate goal is to maximize the stroke such that the majority of the energy is absorbed at the lowest possible load and thus minimizes the forces experienced by an underlying mass, such as the brain.
Non-linear impacts (e.g., off-angle hits) may induce harmful, injurious rotations of the brain relative to the brain stem. Helmet energy absorbers with homogeneous properties tuned for linear impacts are typically so rigid that they fail to stroke substantially and remain “coupled” to the head in a non-linear off-axis event.
While more displacement may be available in the off-angle impact than when an impact is “normal” to the head, this stroke advantage is often wasted. The majority of advanced helmet development testing is currently focused on decoupling the helmet liner from the head. This allows the helmet to slip relative to the skull, thereby reducing the rotation of the brain about the brain stem with traditional energy absorbing materials such as foam.
In one example, 6D Systems developed a single use impact system for motorsports that was well received by the ASTM in a 2013 conference. However, its price point is several times higher than the average helmet liner system, requires replacement after an impact event, exhibits a relatively poor stroke efficiency of less than 65%, and lacks a strain rate response to the incoming impact energy.
Among the art considered before filing this application are these references:
Assignee NameUSPNMaterialRiddell7,954,177FoamBrine7,908,678FoamXenith7,895,681TPUTeam Wendy6,453,476FoamGentex7,958,573FoamMorgan7,802,320FoamCrescendo7,676,854PlasticSkydex6,777,062TPU
Also reviewed were: U.S. Pat. No. 8,353,640; U.S. published application nos. 2013/0152287; 2014/0007322 and 2014/0097052.
Additionally, several of Applicant's patents (see, e.g., U.S. Pat. Nos. 6,199,942; 6,247,745; 6,679,967; 6,682,128; 6,752,450; 7,360,822; 7,377,577; 7,404,593; 7,625,023; 7,625,036; 7,628,444; 8,465,087 and U.S. published applications (see, e.g., 2013/0192286 and 2013/0152287) which are incorporated herein by reference) describe embodiments of an efficient, modular, tunable energy absorbing assembly for reducing the severity of an impact event.
Ideally, a helmet energy absorbing system would be optimized for both low and high energy impact events both normal to and inclined or tangential to the head.
Helmet manufacturers have moved away from foam and into engineered thermoplastic energy absorbing systems. Helmet manufacturers such as Schutt, Zenith, and Cascade/Bauer have recognized the linear impact performance advantages of thermoplastic helmet liners in their helmet systems. However, these systems are largely focused on compliance to established linear impact standards such as NOCSAE, ASTM, and CSA. These standards do not take into account balancing non-linear events with linear events. Nor do they address lower energy impact events such as those experienced in youth sports. Additionally, many of these systems employ a common energy absorbing structure around the entire periphery of the helmets that fails to consider the unique spatial constraints of the impact including the shape of the skull, impact reaction surface, impact angle, and rotation induced in the brain stem based on impact position relative to the head center of gravity.